Method of manufacturing a support for a lithographic printing plate

ABSTRACT

Disclosed is a method of manufacturing a support for a lithographic printing plate, which method includes: a casting step in which an aluminum alloy melt is fed between a pair of cooling rollers by a melt feed nozzle and is rolled as it is being solidified by the pair of cooling rollers, forming an aluminum alloy plate, and a graining treatment step in which a surface of the aluminum alloy plate is subjected to graining treatment which includes at least alkali etching treatment and subsequent electrochemical graining treatment, thereby giving a support for a lithographic printing plate; wherein the surface of the aluminum alloy plate on the side which is subjected to the graining treatment undergoes an amount of aluminum dissolution X per square meter (g/m 2 ) during the alkali etching treatment and has a total amount of electricity Y per square decimeter (C/dm 2 ) applied thereto during an anode reaction in the electrochemical graining treatment such as to satisfy formula (1) below: 1,000&gt;Y≧10X (1). By using this method, a support for a lithographic printing plate which is free of surface mottling is provided.

The entire contents of literatures cited in this specification areincorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a method of manufacturing a support fora lithographic printing plate using an aluminum alloy plate.

Aluminum alloy plate is generally produced by casting a slab from analuminum alloy melt by a semi-continuous casting process, subjecting theslab to homogenizing heat treatment, then hot rolling, cold rolling and,if necessary, annealing. To produce aluminum alloy plate continuously ina simpler operation, various continuous casting processes have beenproposed which use a moving mold to cast an aluminum alloy melt directlyas a plate.

Continuous casting processes which use such a moving mold includeprocesses that employ a moving mold in the form of a pair of belts, suchas the Hazelett process and processes which employ a moving mold in theform of a pair of rolls, such as the Hunter process and the 3C process.In the Hunter process, a pair of cooling rollers are tilted about 15° tothe horizontal and the aluminum alloy plate is cast in an upwardlyangled direction. In the 3C process, a pair of cooling rollers arearranged vertically and the aluminum alloy plate is cast in thehorizontal direction. An advantage with such processes which use movingmolds is that the equipment can be compact. Processes which use movingmolds in the form of rolls are especially outstanding in this respect.

In a process that uses a roll-type moving mold, the aluminum alloy melt(referred to hereinafter as “aluminum melt”) is fed between a pair ofcooling rollers by a melt feed nozzle, and solidification and rolling ofthe aluminum melt are carried out by the cooling rollers as a singleoperation. Processes which use roll-type moving molds are specificallydescribed in U.S. Pat. No. 2,790,216, CA 619,491 B, JP 51-15968 B (theterm “JP XX-XXXXXX B” as used herein means an “examined Japanese patentpublication”), JP 51-89827 A (the term “JP XX-XXXXXX A” as used hereinmeans an “unexamined published Japanese patent application”) and JP58-209449 A.

SUMMARY OF THE INVENTION

However, when supports for lithographic printing plates are manufacturedusing an aluminum alloy plate obtained by these methods, surfacemottling arises.

Accordingly, the object of the present invention is to provide a methodof manufacturing lithographic printing plate supports which are free ofsurface mottling.

The inventors have conducted serious studies in order to achieve theforegoing object and have discovered that when the amount of aluminumdissolution in alkali etching treatment is large, surface mottling tendsto arise, and that this is because mottling caused by host crystals,which are in the uniform crystal structure on the surface, is readilymade visible by alkali etching treatment. “Host crystals,” as usedherein, refers to a group of crystals among the crystal grains in thecasting step which have a relatively similar crystal orientation.

The inventors have also found that, even in such a case, the surfacemottling that has arisen can be reduced by increasing the total amountof electricity during the anode reaction in subsequent electrochemicalgraining treatment. The inventors have learned as well that a totalamount of electricity during the anode reaction in the electrochemicalgraining treatment which is too large diminishes the surface mottlingreducing effect.

Based on these findings, the inventors have completed a method ofmanufacturing a support for a lithographic printing plate of the presentinvention which keeps surface mottling from occurring by, in the courseof graining treatment, setting the total amount of electricity duringthe anode reaction in the electrochemical graining treatment accordingto the amount of aluminum dissolution in the preceding alkali etchingtreatment, and by setting the total amount of electricity during theanode reaction in the electrochemical graining treatment within aspecific range.

Accordingly, the present invention provides the following method ofmanufacturing a support for a lithographic printing plate.

(1) A method of manufacturing a support for a lithographic printingplate, which method includes:

a casting step in which an aluminum alloy melt is fed between a pair ofcooling rollers by a melt feed nozzle and is rolled as it is beingsolidified by the pair of cooling rollers, forming an aluminum alloyplate, and

a graining treatment step in which a surface of the aluminum alloy plateis subjected to graining treatment which includes at least alkalietching treatment and subsequent electrochemical graining treatment,thereby giving a support for a lithographic printing plate;

wherein the surface of the aluminum alloy plate on the side which issubjected to the graining treatment undergoes an amount of aluminumdissolution X per square meter (g/m²) during the alkali etchingtreatment and has a total amount of electricity Y per square decimeter(C/dm²) applied thereto during an anode reaction in the electrochemicalgraining treatment such as to satisfy formula (1) below:1,000>Y≧10X  (1).

(2) The method of manufacturing a support for a lithographic printingplate according to (1) above, wherein the cooling rollers in the castingstep have a circumferential speed V (m/min), the aluminum alloy platehas a thickness t (m), and the cooling rollers have a diameter D (m)which satisfy formula (2) below:V≧5×10⁻⁵×(D/t ²)  (2)

(3) The method of manufacturing a support for a lithographic printingplate according to (1) or (2) above, wherein the melt feed nozzle has anopening with an outer edge that touches the cooling rollers and an outerperiphery in which a relief has been recessed to avoid contact with thecooling rollers.

(4) The method of manufacturing a support for a lithographic printingplate according to any one of (1) to (3) above, wherein at least part ofthe melt feed nozzle is made of a heat-resistant material and wherein aplurality of supporting members composed of a material having a higherflexural strength than the material making up the nozzle are disposed atintervals of up to 200 mm in a width direction on the melt feed nozzleand support a tip of the melt feed nozzle.

(5) The method of manufacturing a support for a lithographic printingplate according to any one of (1) to (4) above, wherein at least part ofthe melt feed nozzle is made of a heat-resistant material having aflexural strength of at least 10 MPa.

(6) The method of manufacturing a support for a lithographic printingplate according to any one of (1) to (5) above, wherein the melt feednozzle has, pre-coated on an inside surface thereof which comes intocontact with the aluminum alloy melt, a release agent containingaggregate particles having a particle size distribution with a mediandiameter of 5 to 20 μm and a mode diameter of 4 to 12 μm.

(7) The method of manufacturing a support for a lithographic printingplate according to any one of (1) to (6) above wherein the melt feednozzle is composed in part of a top plate member which contacts thealuminum alloy melt from above and a bottom member which contacts thealuminum alloy melt from below, each of which members is verticallymovable; and the top plate member and bottom plate member are eachsubjected to pressure by the aluminum alloy melt and thereby pushedagainst an adjoining cooling roller surface.

(8) The method of manufacturing a support for a lithographic printingplate according to any one of (1) to (7) above, which methodadditionally includes, before the casting step, a feeding step in whichthe aluminum alloy melt is fed from a melting and holding furnacethrough a flow channel to the melt feed nozzle;

wherein a stirrer provided in a recess formed in a base of the flowchannel stirs the aluminum alloy melt in the vicinity of the recess.

(9) The method of manufacturing a support for a lithographic printingplate according to any one of (1) to (8) above, wherein, in the alkalietching treatment, X is at least 1 g/m² and an amount of aluminumdissolution per square meter of surface on the side of the aluminumalloy plate not subjected to graining treatment is at least 1 g/m², andwherein Y in the electrochemical graining treatment is at least 50C/dm².

(10) The method of manufacturing a support for a lithographic printingplate according to any one of (1) to (9) above, wherein X in the alkalietching treatment is from 1 to 13 g/m² and an average current densityduring the anode reaction in the electrochemical graining treatment isat least 5 A/dm².

The method of the present invention provides a support for alithographic printing plate which is free of surface mottling.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an exemplary casting arrangementfrom the melting furnace to the casting machine.

FIG. 2 is a schematic diagram showing an example of a recess providedwith a stirrer.

FIG. 3 is a schematic diagram showing another example of a recessprovided with a stirrer.

FIG. 4 is a schematic diagram showing an example of the relativepositions of cooling rollers, a melt feed nozzle, an aluminum alloyplate, an aluminum melt and a melt meniscus.

FIG. 5 is a schematic diagram showing a preferred embodiment of theshape of the melt feed nozzle and the relative positions of the meltfeed nozzle and a cooling roller.

FIG. 6 is a schematic diagram showing an example of a melt feed nozzlehaving supporting members.

FIG. 7 is a schematic diagram showing an example of a melt feed nozzlehaving a tip with a movable construction.

FIG. 8 is a schematic diagram showing another example of a melt feednozzle having a tip with a movable construction.

FIG. 9 is a schematic diagram showing an example of a cold rolling millthat may be used in cold rolling.

FIG. 10 is a schematic diagram showing an example of a straighteningmachine.

FIG. 11 is a schematic diagram showing an example of the shape of a meltfeed nozzle and the relative positions of the melt feed nozzle and acooling roller according to the prior art.

FIG. 12 is a schematic diagram showing another example of a melt feednozzle and the relative positions of the melt feed nozzle and a coolingroller according to the prior art.

FIG. 13 is a schematic diagram showing an example in which the tip ofthe melt feed nozzle has failed.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the inventive method of manufacturing supportsfor lithographic printing plates are described below in conjunction withthe attached drawings.

Cleaning Treatment Step:

First, if necessary, an aluminum melt which has been adjusted to apredetermined composition is subjected to conventional cleaningtreatment. Cleaning treatment, which is carried out to removeunnecessary gases such as hydrogen from the aluminum melt, involves fluxtreatment; degassing treatment using argon gas, chlorine gas or thelike; filtering treatment using, for instance, what is referred to as arigid media filter (e.g., ceramic tube filters, ceramic foam filters), afilter that employs a filter medium such as alumina flakes or aluminaballs, or a glass cloth filter; or a combination of degassing treatmentand filtering treatment.

Cleaning treatment is not essential, but is preferably carried out toprevent defects due to foreign matter such as nonmetallic inclusions andoxides in the aluminum melt, and defects due to dissolved gases withinthe aluminum melt.

Feeding Step:

The feeding step, which is carried out as needed, involves supplying thealuminum melt from a melting furnace to the melt feed nozzle through aflow channel. It is preferable here to have a stirrer provided in arecess formed in the base of the flow channel stir the aluminum melt inthe vicinity of the recess.

If large particles from an upstream source, such as crystal grainrefining agent or a part of refractory material, enter the aluminum meltto be supplied to the melt feed nozzle, the large particles will becomeembedded in the aluminum alloy plate obtained by continuous casting,giving rise to black or blackish-brown streaked mottling when grainingtreatment that includes alkali etching treatment and electrochemicalgraining treatment is carried out.

Therefore, stirring the aluminum melt just before it is supplied to themelt feed nozzle is advantageous for preventing stagnation of thealuminum melt and for preventing the settling and accumulation of largeparticles during stagnation. This is described more fully below.

FIG. 1 is a schematic diagram showing an exemplary casting arrangementfrom the melting furnace to the casting machine. An aluminum melt 22held in a melting furnace 12 is supplied via a flow channel 14 to a meltfeed nozzle 16 in a casting machine 10. A recess 30 is formed in thebase of the flow channel 14 at an intermediate position thereon, and agas discharging element 43 is provided in the recess 30 as the stirrer.

FIG. 2 is a schematic diagram showing an example of a recess providedwith a stirrer.

When casting is continued for a long time, impurities having a highspecific gravity settle to the bottom of the recess 30. Moreover, thealuminum melt has a tendency to be trapped by the stagnation in flowthat occurs at the top of the recess 30 and held there for a while. Asshown in FIG. 2, a gas such as argon that does not react with thealuminum melt 22 is discharged as small bubbles 46 from a gasdischarging element 43 which is made of ceramic or some other porousmaterial and located within the recess 30, thereby agitating thealuminum melt 22 in the recess 30 and preventing stagnation fromoccurring.

FIG. 3 is a schematic diagram showing another example of a recessprovided with a stirrer. As shown in FIG. 3, a gas such as argon thatdoes not react with the aluminum melt 22 is discharged as small bubbles46 from a rotor 45 within the recess 30, thereby agitating the aluminummelt 22 in the recess 30 and preventing stagnation from occurring.

Such mechanisms are described more fully in JP 2000-24762 A.

Casting Step:

In the casting step, the aluminum melt is fed between a pair of coolingrollers by the melt feed nozzle and is rolled as it is being solidifiedby the pair of cooling rollers, forming an aluminum alloy plate.

As shown in FIG. 1, at the casting machine 10, the aluminum melt 22 isfed between a pair of cooling rollers 18 by the melt feed nozzle 16. Thealuminum melt 22 is rolled as it is being solidified by the coolingrollers 18, forming an aluminum alloy plate 36. The resulting aluminumalloy plate 36 has a thickness of preferably 0.1 to 0.5 mm, although thethickness is generally set at 1 to 10 mm when the subsequently describedrolling step is carried out.

FIG. 4 is a schematic diagram showing an example of the relativepositions of the cooling rollers, the melt feed nozzle, the aluminumalloy plate, the aluminum melt and a melt meniscus. In FIG. 4, thealuminum melt 22 passes through a melt feed nozzle 16 composed of a pairof nozzle plates 4 a and 4 b and side plates (not shown), and is fedbetween a pair of cooling rollers 18 that have been installed with aclearance C therebetween, thereby casting an aluminum alloy plate in thedirection of the arrow a. The aluminum melt 22 spreads vertically in thegap defined by top and bottom surfaces at a curvature corresponding tothe nozzle outlet and the diameter of the cooling rollers, therebyforming a melt meniscus 3. In the aluminum melt 22 which comes intocontact with the cooling rollers 18, because heat flows toward thecenter of each of the pair of cooling rollers 18, the crystal structuregrows in the same direction as the flow of heat. The cast aluminum alloyplate has a thickness t which is substantially equal to the clearance Cbetween the cooling rollers 18 or is a value equivalent to the sum ofthe clearance C and elastic deformation by the casting machine and thealuminum alloy plate.

When a roll-type moving mold such as this is used, the moving mold movescontinuously with respect to the aluminum melt that is fed. Hence,unstable contact between the melt and the moving mold during casting andrapid solidification of the aluminum melt following contact with themoving mold tends to destabilize heat flow during solidification. As aresult, growth of the crystal structure becomes non-uniform.

If growth of the crystal structure is non-uniform, large crystal defectsin the form of stripes occur. When rolling and heat treatment have beencarried out and a support for a lithographic printing plate has beenformed, critical defects in appearance such as surface mottling mayarise, regardless of the conditions under which graining treatment iscarried out.

It is preferable for the cooling rollers to have a circumferential speedV (m/min), the aluminum alloy plate to have a thickness t (m) and thecooling rollers to have a diameter D (m) which satisfy formula (2) belowbecause in such a relation surface mottling does not readily arise.

It is especially preferable for these parameters to satisfy formula (2ˆ)below.

Reference may be made to JP 2002-143988 A for further details concerningthe relationship between these parameters.V≧5×10⁻⁵×(D/t ²)  (2)V≧8×10⁻⁵×(D/t ²)  (2′)

If the spacing between the melt feed nozzle and the cooling rollers isunstable, as noted above, contact between the aluminum melt and themoving mold becomes unstable, which tends to destabilize heat flowduring solidification. As a result, growth of the crystal structure isnon-uniform, which in turn leads to defects in the appearance of theresulting support for a lithographic printing plate.

When the melt feed nozzle and the cooling rollers are brought intocontact, the gap between the tip of the melt feed nozzle and the coolingrollers will be unstable unless the place of contact is always the same.Appearance defects in the support for lithographic printing plates willarise in such cases as well.

FIGS. 11 and 12 are schematic diagrams showing examples of the shape ofa melt feed nozzle and the relative positions of the nozzle and acooling roller according to the prior art. In FIG. 11, a nozzle 9 ahaving an ordinary shape is used. The nozzle 9 a and a cooling roller 18are disposed so as to be in mutual contact. In this case, it isdifficult to bring only the tip T of the nozzle 9 a into contact withthe cooling roller 18. As a result, a gap 11 a arises between the tip Tof the nozzle 9 a and the surface of the cooling roller 18. This gap 11a causes the melt meniscus to change readily, which tends to encouragenon-uniform growth of the crystal structure.

A nozzle of ordinary shape is used in FIG. 12 as well. Here, the nozzle9 a and the cooling roller 18 are disposed with a gap 11 b therebetweenand not allowed to touch. Here too, for the same reason as above, themelt meniscus readily changes, encouraging non-uniform growth of thecrystal structure.

However, the inventors have found that appearance defects (e.g., unevensurface solidification) can be effectively suppressed by preventingchanges in the melt meniscus that are caused by the gap between thenozzle and the surfaces of the cooling rollers.

Accordingly, in this invention, it is preferable for the melt feednozzle to have an opening with both an outer edge that touches thecooling rollers and an outer periphery in which a relief has beenrecessed to avoid contact with the cooling rollers. In such anarrangement, only the tip of the melt feed nozzle is constantly in touchwith the cooling rollers, increasing the stability of the melt at thenozzle tip, which is highly desirable.

FIG. 5 is a schematic diagram showing a preferred embodiment of theshape of the melt feed nozzle and the relative positions of the meltfeed nozzle and a cooling roller. In FIG. 5, only the nozzle plate andcooling roller on the upper side of the nozzle are shown, but the samepositional relationship exists between the nozzle plate and coolingroller on the lower side of the nozzle.

In FIG. 5, the outer edge of the melt feed nozzle 16 opening touches thecooling roller 18, and the outer periphery of the melt feed nozzle 16opening has recessed therein a relief (chamfer) to avoid contact withthe cooling roller 18. That is, only the tip T of the melt feed nozzle16 touches the cooling roller 18. The relief (chamfer) is preferablyprovided over the entire width of the melt feed nozzle 16.

By using such a construction, a gap that forms a space where the meltmeniscus may change is not provided. As a result, there can be obtainedan aluminum alloy plate in which appearance defects do not arise. Inturn, a support for a lithographic printing plate in which appearancedefects have been further suppressed can be obtained.

If the melt feed nozzle is of inadequate strength, part of the melt feednozzle may fail during casting. This will change the gap between themelt feed nozzle and the cooling rollers, leading in the same way asdescribed above to surface mottling.

FIG. 13 is a schematic diagram showing an example in which the tip ofthe melt feed nozzle has failed. The melt meniscus is generally locatedin a region like that shown in FIG. 4. However, if the nozzle tips 14 aand 14 b fail due to external causes such as stress, the melt meniscuschanges in a region like that shown in FIG. 13. The meniscus becomesunstable and the melt residence time at the melt meniscus changes, whichtends to lead to crystal in homogeneities such as large crystals.Examples of external causes include unstable solidification immediatelyafter the start of casting, an abnormal rolling load, meander andwaviness of the cast plate, and vibrations.

In the practice of the present invention, it is thus advantageous for atleast part of the melt feed nozzle to be made of a heat-resistantmaterial.

The heat-resistant material is preferably one having a flexural strengthof at least 10 MPa. Engineering-grade fine ceramics are desirablebecause they provide both heat resistance and strength. Morespecifically, ceramic materials which contain at least one materialselected from the group consisting of ZrO₂, Al₂O₃, Si₃N₄, SiC, SiO₂ andaluminolithium silicate are preferred because of their strength and heatresistance. Of these materials, ones having a low thermal conductivityare desirable for avoiding unnecessary cooling of the aluminum alloymelt within the nozzle. From this standpoint, ZrO₂, Al₂O₃ andaluminolithium silicate are preferred. The use of aluminolithiumsilicate as a mixture with calcium silicate is preferable for loweringthe thermal conductivity.

The melt feed nozzle may be made entirely of the above-describedheat-resistant material.

Preferably, a plurality of supporting members composed of a materialhaving a higher flexural strength than the material making up the meltfeed nozzle are disposed at intervals of up to 200 mm along the width ofthe nozzle and support the tip of the melt feed nozzle. This makes thetip harder to deform, reducing the likelihood of melt feed nozzlefailure.

FIG. 6 is a schematic diagram showing an example of a melt feed nozzlehaving supporting members. FIG. 6A is a side view, and FIG. 6B is a topview. As shown in FIG. 6, the melt feed nozzle 16 is supported bysupporting members 15 a. The supporting members 15 a are composed of amaterial having a higher flexural strength than the material making upthe melt feed nozzle 16.

To increase the supporting effect, the interval between the supportingmembers 15 a should preferably be no more than 200. However, for each ofthe supporting members 15 a to provide good support where it is located,an interval of at least 20 mm is preferred. Within this range, tipfailure can be reliably prevented from occurring even when the melt feednozzle 16 is made of a refractory material of relatively low strength(e.g., a flexural strength of less than 10 MPa), such as Marinite orcalcium silicate.

To prevent failure of the melt feed nozzle when working the invention,it is preferable to use both the above-described heat-resistant materialand the above-described supporting members.

When flow by the melt within the melt feed nozzle is turbulent andnon-uniform, crystal inhomogeneities in the form of streaks occurcontinuously or intermittently in the aluminum alloy plate rollingdirection, causing mottling.

In the practice of the present invention, it is thus preferable for themelt feed nozzle to be pre-coated, on the inside surface thereof thatcomes into contact with the aluminum alloy melt, with an aggregateparticle-containing release agent.

The aggregate used as the aggregate particles is preferably boronnitride. It is preferable for the aggregate particles to have a particlesize distribution characterized by a median diameter of 5 to 20 μm and amode diameter of 4 to 12 μm.

In this way, the aluminum melt can be prevented from sticking to theinside surface of the melt feed nozzle and flow within the nozzle can bekept orderly, making it possible to prevent streak-like inhomogeneitiesin growth of the crystal structure.

These phenomena are described more fully in JP 11-192537 A.

In the practice of the present invention, the melt feed nozzle ispreferably composed in part of a top plate member which contacts thealuminum alloy melt from above and a bottom plate member which contactsthe aluminum alloy melt from below, each of which members is verticallymovable. The top plate member and the bottom plate members are eachsubjected to pressure by the aluminum alloy melt and thereby pushedagainst the adjoining cooling roller surface.

This arrangement places the tip of the melt feed nozzle and the coolingroller in constant contact, as a result of which the shape of the meltmeniscus is held constant, thus making it possible to obtain a supportfor lithographic printing plates in which appearance defects are evenfurther suppressed.

FIG. 7 is a schematic diagram showing an example of a melt feed nozzlehaving a tip with a movable construction. FIG. 7A is a top view, andFIG. 7B is a side view.

In the melt feed nozzle 16A shown in FIG. 7, a top plate member 40 and abottom plate member 42 are fixed with bolts 90 in such a way as to allowthe tip of the top plate member 40 and the tip of the bottom platemember 42 to move a little in response to pressure by the aluminum melt.The respective tips of the top plate member 40 and the bottom platemember 42 can thus be brought into contact with the cooling rolls underpressure by the aluminum melt.

FIG. 8 is a schematic diagram showing another example of a melt feednozzle having a tip with a movable construction. FIG. 8A is a top view,and FIG. 8B is a side view.

In the melt feed nozzle 16B shown in FIG. 8, a top plate member 40 and abottom plate member 42 are fixed with pins 92 in such a way as to allowthe tip of the top plate member 40 and the tip of the bottom platemember 42 to pivot a little about the respective pins 92 in response topressure by the aluminum melt. The respective tips of the top platemember 40 and the bottom plate member 42 can thus be brought intocontact with the cooling rolls under pressure by the aluminum melt.

These mechanisms are described more fully in JP 2000-117402 A.

Rolling Step:

Following the above casting step, it is preferable to carry out arolling step in which the aluminum alloy plate is cold rolled to adesired thickness. Cold rolling further reduces the thickness of thealuminum alloy plate obtained in the casting step. To achieve bettercold rolling efficiency, it is advantageous for the aluminum alloy plateobtained in the casting step to have a small thickness.

FIG. 9 is a schematic diagram showing an example of a cold rolling millthat may be used to cold roll the cast aluminum alloy plate. The coldrolling mill 50 shown in FIG. 9 carries out cold rolling by using a pairof cold-rolling rollers 56, each of which is rotated by a supportingroller 58, to apply pressure to an aluminum alloy plate 36 which travelsbetween a delivery coil 52 and a take-up coil 54.

After cold rolling, it is desirable to carry out intermediate annealing,a type of heat treatment, so as to achieve a finer aluminum metalcrystal structure, then to carry out cold rolling once again.

This rolling step is advantageous for bringing the aluminum alloy plateto a final thickness of 0.1 to 0.5 mm suitable for use as a support forlithographic printing plates.

The finished aluminum alloy plate may be subjected to a straighteningstep which improves flatness by means of a straightening machine such asa roller leveler or a tension leveler. A slitting step in which theplate is passed through a slitter line is also generally carried out tocut the plate to a predetermined width.

FIG. 10 is a schematic diagram showing an example of a straighteningmachine. The straightening machine 70 shown in FIG. 10 improves theflatness of an aluminum alloy plate 36 traveling between a delivery coil82 and a take-up coil 84 while applying tension with a leveler 80 thatincludes work rolls 86. The plate is then cut to a predetermined widthwith a slitter 88.

Graining Step:

In the graining step, the surface of the aluminum alloy plate obtainedfrom the previous steps is subjected to graining treatment whichincludes at least alkali etching treatment followed by electrochemicalgraining treatment, thereby giving a support for a lithographic printingplate.

Various methods for the suppression of mottling have already beenmentioned in the description of the casting step. When these methodsalone are used, while the crystal structure prior to graining treatmentwill appear uniform, if a particularly large amount of alkali etchingoccurs after graining treatment, any history of non-uniformity in thecrystal structure will tend to be revealed.

The inventors have found that by establishing a specific relationshipbetween the amount of aluminum dissolved in alkali etching treatment andthe total amount of electricity during the anode reaction inelectrochemical graining treatment, a uniform crystal structure can beachieved even after graining treatment. Moreover, in practicing thepresent invention, mottling can be suppressed even further byestablishing a specific relationship between the amount of aluminumdissolved in alkali etching treatment and the total amount ofelectricity during the anode reaction in electrochemical grainingtreatment and using in combination with this any of the various methodsfor the suppression of mottling described above in connection with thecasting step.

Graining treatment generally consists of one or a combination of two ormore of the followings: mechanical graining, chemical graining andelectrochemical graining.

In the practice of the present invention, graining treatment includesboth alkali etching treatment and subsequent electrochemical grainingtreatment, although it may also include other types of grainingtreatment. The various types of treatments that may be included ingraining treatment are described below.

Mechanical Graining:

Mechanical graining is carried out to give the surface of the aluminumalloy plate an average surface roughness of 0.35 to 1.0 μm. Methods suchas those described in JP 6-135175 A and JP 50-40047 B may be used tocarry out mechanical graining. This type of treatment is preferablycarried out before electrochemical graining (before the firstelectrochemical graining treatment if electrochemical graining iscarried out a plurality of times).

Mechanical graining preferably involves the use of a rotating nylonbrush roll having a bristle diameter of 0.2 to 0.9 mm and an abrasivecompound that is supplied as a slurry to the surface of the aluminumalloy plate. Use may also be made of a technique that involves blowingthe slurry onto the surface of the plate, a technique that involves theuse of a wire brush, or a technique in which the pattern-indentedsurface shape of a reduction roll is transferred to the aluminum alloyplate. The last of these methods is better than methods which use abrush or abrasive compound because there is less tendency for locallydeep areas to form.

In cases where the average surface roughness is to be set to less than0.35 μm, mechanical graining treatment is generally not carried out.

Chemical Etching:

In chemical etching treatment, the surface of the aluminum alloy plateis chemically etched in an alkaline or acidic aqueous solution. In thepractice of the invention, alkali etching treatment having an excellentdissolution efficiency is carried out using an alkaline aqueoussolution. A known method may be used to carry out alkali etchingtreatment. In the invention, alkali etching treatment is carried outbefore the first electrochemical graining treatment.

Alkali etching treatment is carried out to dissolve the uneven edgesthat form on the surface of the plate during mechanical grainingtreatment, so as to obtain a smoothly undulating surface. As a result,lithographic printing plates of excellent scumming resistance can beobtained.

In cases where mechanical graining treatment has not been carried out,alkali etching treatment is used to remove foreign matter such asrolling oils remaining on the surface of the aluminum alloy plate.

Illustrative examples of alkaline aqueous solutions that may be used inalkali etching treatment include aqueous solutions containing one ormore of the followings: sodium hydroxide, sodium carbonate, sodiumaluminate, sodium metasilicate, sodium phosphate, potassium hydroxideand lithium hydroxide. An aqueous solution composed mainly of sodiumhydroxide is especially preferred. The alkaline aqueous solution maycontain 0.5 to 10 wt % of aluminum and also alloying ingredients presentin the aluminum alloy plate.

The alkaline aqueous solution has a concentration of preferably 1 to 50wt %, and more preferably 1 to 30 wt %.

It is advantageous to carry out alkali etching treatment for 1 to 120seconds, and preferably 2 to 60 seconds, at an alkaline aqueous solutiontemperature in a range of 20 to 100° C., and preferably 40 to 80° C.

The amount of aluminum dissolution in alkali etching treatment followingmechanical graining treatment is preferably 1 to 20 g/m² at the surfaceon the side of the aluminum alloy plate subjected to graining treatment.Excessive alkali etching treatment is undesirable because mottling dueto host crystals present within the aluminum alloy plate readily arises.Hence, the amount of aluminum dissolution is preferably 1 to 13 g/m²,and more preferably 2 to 13 g/m².

When mechanical graining treatment has not been carried out, it ispreferable for the amount of aluminum dissolution to be 1 to 6 g/m² atthe surface of the aluminum alloy plate on the side that is subjected tograining treatment.

As described above, by having the amount of aluminum dissolution at thesurface of the aluminum alloy plate on the side where graining treatmentis performed be at least 1 g/m², impurities near the surface layer ofthe aluminum alloy plate can be completely removed, enabling uniformelectrochemical graining treatment to be carried out.

It is preferable for the amount of aluminum dissolution at the surfaceof the aluminum alloy plate on the side that is not subjected tograining treatment, i.e., the back side, to be at least 1 g/m².

There is no direct relationship between the back side of a lithographicprinting plate and its performance. However, when an image recordinglayer is provided on the support for lithographic printing plate to forma presensitized plate and the presensitized plate is wound up into acoil or cut into sheets and stacked, impurities near the surface layeron the back side of a plate come into contact with, and may causedefects in, the image-recording layer on the adjoining plate. By settingthe amount of aluminum dissolution on the back side within theabove-indicated range, impurities near the surface layer on the backside can be removed, making it possible to prevent such defects fromoccurring in the image recording layer.

The relationship between the amount of aluminum dissolution duringalkali etching treatment at the surface of the aluminum alloy plate onthe side which is subjected to graining treatment and the total amountof electricity during the anode reaction in electrochemical grainingtreatment at the surface of the aluminum alloy plate on the sidesubjected to graining treatment shall be described later in thespecification.

Electrochemical Graining:

Electrochemical graining is a treatment in which an alternating currentor a direct current is passed through the aluminum alloy plate as theelectrode in an acidic aqueous solution so as to electrochemically grainthe surface of the plate. Electrochemical graining may be carried outusing a method known to the art.

Electrochemical graining is carried out with the aim of formingcrater-like or honeycomb-like pits having an average diameter of about0.05 to 20 μm to a surface area ratio of 30 to 100% on the surface ofthe aluminum alloy plate. Electrochemical graining treatment enhancesthe press life and the scumming resistance in non-image areas of thelithographic printing plate.

Any acidic aqueous solution used in conventional electrochemicalgraining involving the use of direct current or alternating current maybe employed here in electrochemical graining treatment, although the useof an acidic aqueous solution composed mainly of nitric acid or anacidic aqueous solution composed mainly of hydrochloric acid ispreferred.

For example, use can be made of a nitric acid-containing acidic aqueoussolution prepared by adding to a nitric acid solution having a nitricacid concentration of 1 to 100 g/L at least one nitrate compound havingnitrate ions, such as aluminum nitrate, sodium nitrate or ammoniumnitrate, to a concentration of from 0.01 g/L to saturation. The nitricacid-containing acidic aqueous solution may also contain, dissolvedtherein, metals which are present in the aluminum alloy, such as iron,copper, manganese, nickel, titanium, magnesium and silicon.

Alternatively, use can be made of a hydrochloric acid-containing acidicaqueous solution prepared by adding to a hydrochloric acid solutionhaving a hydrochloric acid concentration of 1 to 100 g/L at least onechloride compound containing chloride ions, such as aluminum chloride,sodium chloride or ammonium chloride, to a concentration of from 0.01g/L to saturation. The acidic aqueous solution composed mainly ofhydrochloric acid may also contain, dissolved therein, metals which arepresent in the aluminum alloy, such as iron, copper, manganese, nickel,titanium, magnesium and silicon.

[0057-0058]

In the practice of the present invention, electrochemical grainingtreatment is performed in such a way that the surface of the aluminumalloy plate subjected to graining treatment undergoes an amount ofaluminum dissolution X per square meter (g/m²) during alkali etchingtreatment and has a total amount of electricity Y per square decimeter(C/dm²) applied thereto during the anode reaction in electrochemicalgraining treatment which satisfy formula (1) below.1,000>Y≧10X  (1)

Thus, in cases where the amount of aluminum dissolution in alkalietching treatment is large, mottling of the support for lithographicprinting plate caused by host crystals that form during casting can beprevented by making the total amount of electricity during the anodereaction in electrochemical graining large. If the total amount ofelectricity during the anode reaction in electrochemical graining is toolarge, the surface mottling reducing effect diminishes. However, byhaving this value fall within the above range, a larger effect can beachieved.

The total amount of electricity during the anode reaction at the surfaceon the side of the aluminum alloy plate subjected to graining treatmentin electrochemical graining is preferably at least 50 C/dm². Within thisrange, mottling at the surface of the support for lithographic printingplate can be more reliably suppressed.

The average current density during the anode reaction in electrochemicalgraining treatment is preferably at least 5 A/dm². Within this range,pit dispersibility in electrochemical graining is good.

Electropolishing Treatment or Second Chemical Etching Treatment:

Electropolishing is a treatment in which electrolysis is carried out inan acidic aqueous solution using the aluminum alloy plate as theelectrode. Any electropolishing method known to the art may be used.

Electropolishing treatment or second chemical etching treatment iscarried out to remove smut consisting primarily of aluminum hydroxidethat has formed in electrochemical graining treatment, and to smooth theedges of the pits that have formed and thereby improve scummingresistance during use as a lithographic printing plate.

The amount of dissolution from the aluminum alloy plate inelectropolishing treatment or the second chemical etching treatment ispreferably 0.05 to 5 g/m², and more preferably 0.1 to 3 g/m². In thepractice of the invention, the amount of aluminum dissolution during thefirst alkali etching treatment must satisfy above formula (1), but noparticular limitation is imposed on the amount of aluminum dissolutionin the second alkali etching treatment.

Following the first and the second and any subsequent alkali etchingtreatments, it is advantageous to carry out desmutting treatment usingan acidic solution.

Anodizing Treatment:

Anodizing treatment is performed to increase the wear resistance at thesurface of the aluminum alloy plate. Anodizing treatment can be carriedout by any method used in the art to which the invention relates. Forexample, an anodized layer can be formed on the surface of the aluminumalloy plate by passing a current through the plate as the anode in asolution having a sulfuric acid concentration of 50 to 300 g/L andhaving an aluminum concentration of up to 5 wt %. The solution used inanodizing treatment is not subject to any particular limitation so longas it can form an oxide layer on the aluminum alloy plate. Illustrativeexamples include solutions of sulfuric acid, phosphoric acid, oxalicacid, chromic acid, or mixtures thereof. The electrolyte concentrationmay be selected as appropriate for the type of electrolyte.

The anodizing treatment conditions vary empirically according to theelectrolytic solution used, although it is generally suitable for thesolution to have a concentration of 1 to 80 wt % and a temperature of 5to 70° C., and for the current density to be 1 to 60 A/dm², the voltageto be 1 to 100 V, and the electrolysis time to be 10 to 300 seconds.These conditions are adjusted to obtain the desired anodized layerweight.

Sealing Treatment:

Sealing treatment is carried out to seal micropore openings in theanodized layer that has been formed by anodizing treatment.

Illustrative examples of sealing treatment include a method in which thealuminum alloy plate is immersed in hot water and an aqueous solutioncontaining an inorganic or organic salt, and a method in which thealuminum alloy plate is passed through a steam bath.

Hydrophilizing Treatment:

Hydrophilizing treatment involves rendering the surface of the supportfor lithographic printing plate hydrophilic.

Illustrative examples of hydrophilizing treatment include the alkalimetal silicate (e.g., aqueous sodium silicate solution) methodsdescribed in U.S. Pat. No. 2,714,066, U.S. Pat. No. 3,181,461, U.S. Pat.No. 3,280,734 and U.S. Pat. No. 3,902,734. In this type of method, thealuminum alloy plate is immersed, or subjected to electrolysis, in anaqueous solution of sodium silicate.

Use can also be made of methods involving treatment with potassiumfluorozirconate as described in JP 36-22063 B, and methods involvingtreatment with polyvinylphosphonic acid, as described in U.S. Pat. No.3,276,868, U.S. Pat. No. 4,153,461 and U.S. Pat. No. 4,689,272.

Presensitized Plate:

The support for lithographic printing plate obtained as described aboveis then provided with an image recording layer, thereby giving apresensitized plate.

The image recording layer is not subject to any particular limitation.Any image recording layer known to the art may be used. Illustrativeexamples include prior-art photosensitive layers that are combined withlith film and exposed to light, thermal-type heat-sensitive layerscapable of direct image formation using a laser, non-treatment typeimage recording layers which do not need to be developed following laserexposure, and image recording layers which can be developed on pressfollowing laser exposure. The image recording layer may be eithernegative-working or positive-working.

For example, the various image recording layers mentioned in JP 6-135175A can be used. Thermal-type heat-sensitive layers that may be usedinclude the image recording layers mentioned in JP 2003-21906 A.

Before providing the image recording layer, an undercoat (intermediatelayer) may be provided, if necessary. Any undercoat known to the art maybe used. Specific examples include those mentioned in JP 6-135175 A.

The presensitized plate obtained by providing an image recording layeron the support for lithographic printing plate is subjected toplatemaking treatment according to the type of image recording layer,thereby forming a lithographic printing plate which can be furnished forprinting. Lithographic printing plates made using supports obtained bythe method of the invention have an excellent printing performance.

EXAMPLES

Examples are given below by way of illustration and not by way oflimitation.

1. Production of Supports for Lithographic Printing Plates

Examples 1 to 8, and Comparative Examples 1 to 10

Supports for lithographic printing plates were produced by carrying outa feeding step, a casting step, a rolling step and a graining treatmentstep in the manner described below.

First, an aluminum alloy plate was continuously cast using thearrangement shown in FIG. 1. To begin with, in the feeding step,aluminum melt that had been subjected to cleaning treatment was suppliedfrom a melting furnace to a melt feed nozzle through a flow channelhaving a stirrer within a recess as shown in FIG. 3. Next, in thecasting step, the aluminum melt was fed by the melt feed nozzle betweena pair of cooling rollers, and was formed into an aluminum alloy plateby rolling the melt as it was being solidified with the pair of coolingrollers.

The circumferential speed V of the cooling rollers and the thickness tof the aluminum alloy plate are given in Table 1. The diameter D of thecooling rollers was 0.9 m.

Table 1 indicates whether or not the outer edge of the melt feed nozzleopening was in contact with the cooling rollers. In cases where therewas contact, use was made of a melt feed nozzle like that shown in FIG.7 which consisted in part of a top plate member that contacted thealuminum melt from above and a bottom plate member that contacted thealuminum melt from below, both plate members being vertically movable.In this nozzle, the top and bottom plate member were each subjected topressure by the aluminum melt and thereby pushed against the surface ofthe adjoining cooling roller.

As shown in FIGS. 5 and 6, the outer periphery of the melt feed nozzleopening had a relief recessed therein to avoid contact with the coolingrollers.

The material making up the melt feed nozzle is shown in Table 1. Themeanings of the symbols shown in Table 1 are explained in Table 2.

Table 1 indicates whether the melt feed nozzle had supporting members.In cases where the nozzle had supporting members, a plurality of suchmembers were disposed at intervals of 180 mm in the width direction.

The release agent on the inside surface of the melt feed nozzle whichcomes into contact with the aluminum melt is shown in Table 1. Themeanings of the symbols shown in Table 1 are explained in Table 3.

In the rolling step, the cast aluminum alloy plate was cold rolled to athickness of 2 mm, after which it was heat treated at 550° C. for 10hours, then was again cold rolled, this time to a final thickness of 0.3mm.

In the graining treatment step, the cold-rolled aluminum alloy plate wassubjected to graining treatment as described below, giving a support fora lithographic printing plate in each example.

First, alkali etching treatment was carried out using an aqueoussolution of sodium hydroxide. The amount of aluminum dissolution was setto different levels by varying the concentration and temperature of theaqueous solution and the treatment time. The amount of aluminumdissolution X at the surface on the side subjected to graining treatmentand the amount of aluminum dissolution on the back side are eachindicated in Table 1.

After rinsing with water, desmutting treatment was carried out using a 1wt % aqueous solution of nitric acid.

Next, electrochemical graining treatment was carried out using analternating current power supply and an aqueous solution of nitric acid.The total amount of electricity Y during the anode reaction inelectrochemical graining treatment is shown in Table 1. The averagecurrent density during the anode reaction in electrochemical grainingtreatment was 20 A/dm².

Next, alkali etching treatment was carried out using an aqueous solutionof sodium hydroxide. The amount of aluminum dissolution at the surfaceon the side subjected to graining treatment was set at 1 g/m².

In addition, desmutting treatment was carried out using a 170 g/Laqueous sulfuric acid solution.

Anodizing treatment was then carried out in a 170 g/L aqueous sulfuricacid solution such as to provide an anodized layer having a weight of2.7 g/m², thereby giving a support for a lithographic printing plate.TABLE 1 Graining treatment step Casting Step Total amount ThicknessContact Release Amount of of electricity t of between agent Amount ofaluminum Y during aluminum tip of on aluminum dissolution anode alloyCircum- melt inner dissolution on back reaction plate ferential feedSupporting surface X in side in electro- Feeding after speed V of nozzleMelt members of alkali in alkali chemical step casting cooling and feedon melt melt etching etching graining Stir- step rollers cooling nozzlefeed feed treatment treatment treatment ring (mm) (m/min) rollersmaterial nozzle nozzle (g/m²) (g/m²) (C/dm²) EX 1 yes 5 2.3 contact 1yes A 6 2 120 EX 2 yes 5 2.3 contact 1 yes A 6 2 70 EX 3 yes 5 2.3contact 1 yes A 6 2 250 EX 4 yes 5 2.3 contact 1 yes A 6 2 500 EX 5 yes5 2.3 contact 1 yes A 6 2 750 EX 6 yes 5 2.3 contact 1 yes A 6 2 900 EX7 yes 3 5.5 contact 1 yes A 6 2 250 EX 8 yes 3 5.5 contact 2 no A 6 2120 CE 1 yes 5 2.3 contact 1 yes A 13 4 120 CE 2 yes 5 1.5 contact 1 yesA 7 2 65 CE 3 yes 5 2.3 no contact 1 yes A 7 2 65 CE 4 yes 3 4.5 contact1 yes A 7 2 65 CE 5 yes 5 2.3 contact 1 no A 7 2 65 CE 6 yes 5 2.3contact 1 yes B 7 2 65 CE 7 yes 5 2.3 contact 1 yes no 7 2 65 CE 8 no 52.3 contact 1 yes A 7 2 65 CE 9 yes 5 2.3 contact 1 yes A 13 4 1,050 CE10 yes 5 2.3 contact 1 yes A 13 0.5 120

TABLE 2 Melt feed Flexural nozzle material Type of material strength(MPa) 1 calcium silicate 9 2 aluminolithium silicate + calcium 100silicate

TABLE 3 Release Median diameter Mode diameter Main agent (μm) (μm)component A 6.5 10.0 boron nitride B 1.5 1.5 zirconium oxide2. Evaluation of Supports for Lithographic Printing Plates

Production of a support for a lithographic printing plate, consisting ofthe above-described feeding step, casting step, rolling step andgraining treatment step, was carried out three times each in therespective examples of the invention and comparative examples. Theresulting supports obtained in each example were evaluated as describedbelow.

(1) Occurrence of Mottling:

The surface of the support for lithographic printing plate was visuallyexamined to determine whether mottling had occurred. “Mottling,” as usedherein, refers to the existence of areas on the surface of the supportfor lithographic printing plate where the glossiness or color tonediffers from that in surrounding areas. The mottling evaluation resultsobtained are shown in Table 4. Here, “occurred” signifies that mottlingclearly occurred in one or more of the three specimens obtained in aparticular example, “slight” signifies that mottling occurred but was ofsuch a slight degree as to be of no concern, and “did not occur”signifies that no mottling whatsoever was observed.

(2) Surface Quality

The surface quality of the support for lithographic printing plate wasvisually examined and rated on a scale of 1 to 6, based collectively onthree surface characteristics of the support for lithographic printingplate: roughness, streaking and mottling. A rating of 6 represents anexcellent surface quality, 5 represents a good surface quality, 4indicates a surface quality that is acceptable for practical purposes, 3indicates a surface quality that is unacceptable for practical purposes,2 signifies a poor surface quality, and 1 signifies a very poor surfacequality.

The rating shown in Table 4 for each example was the worst ratingobtained for the three specimens in that example.

(3) Stability of Surface Quality

A surface quality stability rating of 3 indicates that all threespecimens produced in a particular example had the same surface qualityrating, a stability rating of 2 indicates that two different surfacequality ratings were obtained among the three specimens, and a stabilityrating of 1 indicates that three different surface quality ratings wereobtained.

These results are shown in Table 4. A higher rating number indicates abetter surface quality stability.

(4) Production Stability

The production stability was rated based on whether, in the castingstep, an aluminum alloy plate could be stably cast without anomaliesoccurring thereon. For the three specimens obtained in each example, arating of 1 was assigned when casting was stopped due to the occurrenceof anomalies in the production of at least one specimen, a rating of 2was assigned when casting was not stopped but anomalies appeared in atleast one of the specimens, and a rating of 3 was assigned when noanomalies appeared in any of the specimens.

These results are shown in Table 4. In Table 4, a higher rating numberindicates better production stability.

As is apparent from Table 4, surface mottling was not observed in thesupports for lithographic printing plates obtained by the method of thepresent invention. Moreover, the surface qualities, stability of thesurface qualities, and production stability were good in each of thesupports obtained according to the method of the present invention.TABLE 4 Stability of Appearance Surface surface Production of mottlingqualities qualities stability Example 1 did not occur 5 3 3 Example 2slight 4 3 3 Example 3 did not occur 6 3 3 Example 4 did not occur 6 3 3Example 5 did not occur 5 3 3 Example 6 did not occur 4 3 3 Example 7did not occur 6 3 3 Example 8 did not occur 5 3 3 Comparative occurred 32 2 Example 1 Comparative occurred 2 1 2 Example 2 Comparative occurred2 1 2 Example 3 Comparative occurred 2 1 2 Example 4 Comparativeoccurred 1 1 1 Example 5 Comparative occurred 1 1 2 Example 6Comparative occurred 1 1 1 Example 7 Comparative occurred 1 1 3 Example8 Comparative occurred 3 2 1 Example 9 Comparative occurred 3 2 1Example 10

1. A method of manufacturing a support for a lithographic printingplate, which method includes: a casting step in which an aluminum alloymelt is fed between a pair of cooling rollers by a melt feed nozzle andis rolled as it is being solidified by the pair of cooling rollers,forming an aluminum alloy plate, and a graining treatment step in whicha surface of the aluminum alloy plate is subjected to graining treatmentwhich includes at least alkali etching treatment and subsequentelectrochemical graining treatment, thereby giving a support for alithographic printing plate; wherein the surface of the aluminum alloyplate on the side which is subjected to the graining treatment undergoesan amount of aluminum dissolution X per square meter (g/m²) during thealkali etching treatment and has a total amount of electricity Y persquare decimeter (C/dm²) applied thereto during an anode reaction in theelectrochemical graining treatment such as to satisfy formula (1) below:1,000>Y≧10X  (1).
 2. The method of manufacturing a support for alithographic printing plate according to claim 1, wherein the coolingrollers in the casting step have a circumferential speed V (m/min), thealuminum alloy plate has a thickness t (m), and the cooling rollers havea diameter D (m) which satisfy formula (2) below:V≧5×10⁻⁵×(D/t ²)  (2).
 3. The method of manufacturing a support for alithographic printing plate according to claim 1, wherein the melt feednozzle has an opening with an outer edge that touches the coolingrollers and an outer periphery in which a relief has been recessed toavoid contact with the cooling rollers.
 4. The method of manufacturing asupport for a lithographic printing plate according to claim 1, whereinat least part of the melt feed nozzle is made of a heat-resistantmaterial and wherein a plurality of supporting members composed of amaterial having a higher flexural strength than the material making upthe nozzle are disposed at intervals of up to 200 mm in a widthdirection on the melt feed nozzle and support a tip of the melt feednozzle.
 5. The method of manufacturing a support for a lithographicprinting plate according to claim 1, wherein at least part of the meltfeed nozzle is made of a heat-resistant material having a flexuralstrength of at least 10 MPa.
 6. The method of manufacturing a supportfor a lithographic printing plate according to claim 1, wherein the meltfeed nozzle has, pre-coated on an inside surface thereof which comesinto contact with the aluminum alloy melt, a release agent containingaggregate particles having a particle size distribution with a mediandiameter of 5 to 20 μm and a mode diameter of 4 to 12 μm.
 7. The methodof manufacturing a support for a lithographic printing plate accordingto claim 1, wherein the melt feed nozzle is composed in part of a topplate member which contacts the aluminum alloy melt from above and abottom member which contacts the aluminum alloy melt from below, each ofwhich members is vertically movable; and the top plate member and bottomplate member are each subjected to pressure by the aluminum alloy meltand thereby pushed against an adjoining cooling roller surface.
 8. Themethod of manufacturing a support for a lithographic printing plateaccording to claim 1, which method additionally includes, before thecasting step, a feeding step in which the aluminum alloy melt is fedfrom a melting and holding furnace through a flow channel to the meltfeed nozzle; wherein a stirrer provided in a recess formed in a base ofthe flow channel stirs the aluminum alloy melt in the vicinity of therecess.
 9. The method of manufacturing a support for a lithographicprinting plate according to claim 1, wherein, in the alkali etchingtreatment, X is at least 1 g/m² and an amount of aluminum dissolutionper square meter of surface on the side of the aluminum alloy plate notsubjected to graining treatment is at least 1 g/m², and wherein Y in theelectrochemical graining treatment is at least 50 C/dm².
 10. The methodof manufacturing a support for a lithographic printing plate accordingto claim 1, wherein X in the alkali etching treatment is from 1 to 13g/m² and an average current density during the anode reaction in theelectrochemical graining treatment is at least 5 A/dm².